A Nonlinear Softening Load-Transfer Approach for the Thermomechanical Analysis of Energy Piles

Energy piles are a profitable solution for extracting shallow geothermal energy and have recently attracted increasing attention. However, the thermomechanical response of energy piles considering shaft resistance softening has not been sufficiently studied, which hinders the perfection of design methods for energy piles. To this end, an improved generalized nonlinear softening model was first developed to describe the thermomechanical loading-unloading-reloading response of energy piles. The parameters of the improved model can be easily calibrated using an interface direct shear test. We then proposed a nonlinear load-transfer approach for the thermomechanical analysis of energy piles considering the softening behavior of skin resistance by continuously describing the nonlinear load-transfer regime. The proposed approach was validated by comparing it with experimental measurements and other numerical methods. Finally, a parametric study was performed to assess the effects of various related parameters on the thermomechanical response of the energy pile. The results indicate that the proposed approach enriches the current methods for energy pile design and provides a helpful tool for obtaining the thermomechanical behavior of energy piles in the case of softening.